ucharclasses – Font actions in XeTeX according to what is being processed

The pack­age takes care of switch­ing fonts when you switch from one
Uni­code block to an­other in the text of a doc­u­ment. This way, you
can write a doc­u­ment with no ex­plicit font se­lec­tion, but a se­ries
of rules of the form “when en­ter­ing block …, switch font to use …”.